In one type of xerographic copying device that is commonly employed, as illustrated in FIG. 1, the platen 10 that receives the document 11 to be copied is fixedly mounted, and movable elongated lamps 12 illuminate a transversely extending strip of the document. This strip of the document is imaged onto a photoreceptor drum 13 via mirrors 14, 15 and 16, a spherical copier lens 15 and a further mirror 17. The mirrors 14, 15 and 16 are moved lengthwise of the document, along with the illuminating lamp, in synchronism with rotation of the drum 13, in accordance with a given relationship, in order to scan the image of the document onto the drum. For example, the mirrors 15, 16 may be moved in the same direction and at half the speed as the mirror 14. The driving of the mirrors and the lamps may be effected in any conventional manner, for example as illustrated in FIG. 2. As illustrated, a scan drive motor 20 drives a belt 21 to pass around two fixed pulleys 22, 23. One end 24 is fixed, and the belt proceeds from this end around a movable pulley 25. and thence to the pulleys 22 and 23. The mirror is affixed to a carriage driven by the belt between the pulleys 22 and 25 so that the mirror 14 is moved at the same speed as the belt. The mirrors 15, 16 are mounted to a further movable carriage that also carries a pulley 26. The belt proceeds from the pulley 23 about the pulley 26. The other end 28 of the belt is spring tensioned. As a consequence, the mirrors 15, 16 are driven in the same direction as the mirror 14, but at half the speed thereof. The speed of the motor 20 is synchronized with the rotation of the photoreceptor drum of the apparatus. A copying device of this design is disclosed, for example, in U.S. Pat. No. 4,188,113.
In order to adapt this type of system to the production of signals for fax transmission, the above patent discloses the imaging of a light spot from a laser onto the document via a rotary polygonal mirror, a separate lens, and the same longitudinally movable mirrors that are employed for conventional document copying. The rotary polygonal mirror effects the transvers scanning of the document. In this arrangement, the light from the imaged spot is reflected to a fiber optic bundle that directs the light to a photomultiplier. In a modification of this arrangement, light from the linear lamp that is employed in the copier mode is directed to one or more photomultiplier tubes via the movable copier mirrors, the separate lens, and the rotary polygonal mirror.
In the arrangement disclosed in this patent, in order to employ the apparatus in the fax mode, it is necessary to adjust the positions of the copier lens and the additional lens, as well as other optical elements. Additionally, the copy image resolution in such systems is limited by the digital image resolution. The requirement for adequate copy resolution leads to a high system cost.